Unless I'm mistaken, NSP stands for National Selection Panel.
As far as I can remember, NSP covered EFLHR, WWLHR and WWLGW but not EFLGW (previously known as EuroGatwick until it's merger with BA Cityflyer, the 90s version).
EuroGatwick was created when BA purchased Dan Air in 1991 and was firmly held in "wholly owned subsidury" status which kept crews on lower paid, harder working contracts. They were not included in the NSP, for a variety of reasons, costs being a major one I would imagine.
EuroGatwick crew were allowed to transfer to EF LHR at a rate of 50 per year and they lost rank and seniority in the process, although they kept their basic salary and date of joining for staff travel purposes.
WWLGW has been disolved (with crew transferring to LHR) and Single Fleet LGW being created out of EFLGW. Current crew would be better placed to comment on whether they are or will be part of the NSP. If SFLGW does become NSP then these crew will have to be considered when it comes to internal fleet transfers.